Carotenoids broadly exist in the nature. They include β-carotene, astaxanthin, canthaxanthin and lycopene. These substances are essential coloring agents used in industries such as food, cosmetics, animal feed stuffs and pharmaceutical industry. In addition, some of them are precursors of vitamin A. Carotenoids are substances which are insoluble in water and are almost insoluble in oil as well. Moreover, carotenoids are substances which are sensitive to heat and oxygen. Therefore, carotenoids are difficult to be absorbed by animals in the form of crystalline coarse particles. Either used in food or other areas, carotenoids in general need to be fine particles and require protective colloid to prevent oxidation. For the purpose of coloration, carotenoids are expected to be improved in bioavailability after being made into preparation to improve the effect of coloration, reduce the amount and minimize the losses in use.
Carotenoids are often made into water-dispersible preparation in using. For this purpose, some literatures have reported various methods of such preparations.
WO091/06292 and WO94/19411 described a method wherein β-carotene is ground into particles with the particle size of 2-10 μm using colloid mill and then is dried to be water-dispersible carotenoid powders. While the grinding efficiency is low, the power consumption is obvious and it is difficult to make the particle size of carotenoids less than 1 μm.
U.S. Pat. No. 3,998,753 described a kind of preparation method of water-dispersible carotenoids with a granularity of less than 1 μm. In this method, carotenoids and other additives are firstly mixed to form an organic solvent solution, which is added into the aqueous solution containing gelatin, dispersant and stabilizer, then the system is made into an emulsion through high speed shear; finally organic solvents are removed and required powders are obtained after spray drying.
In EP-0065193 (or U.S. Pat. No. 4,522,743) recorded a preparation method of water-dispersible carotenoid powders. First, carotenoids are dissolved in a volatile water-miscible solvent in 10 seconds at 50-200° C. and rapidly mixed with the aqueous solution containing protective colloid at 0-50° C., so carotenoids with the particle size of less than 0.5 μm are dispersed in the protective colloid, then carotenoid powders can be obtained after removing solvents and drying. The process requires high pressure (3.0-6.0 MPa) and high temperature (170-200° C.). This process has strict requirements for equipment and is difficult to operate and control.
In the above-mentioned methods using solvents or high temperature solvents, it is necessary to remove a large volume of solvents from the protective colloid system. The process takes a long time and thorough removal is not easy. The system will easily blister when being heated and precipitated in the presence of protective colloid, with a very low efficiency of precipitation. It is difficult to control the particle size and the content of trans isomer of required carotenoid powders.
Because of the problems existing in the above patents, the applicant of the present invention applied for a preparation method of water-dispersible carotenoid powders in 2005 (the publication number of the patent is CN1836652A). In the method, coarse carotenoid crystals are firstly dissolved in halogenated hydrocarbon or esters which contain antioxidants and emulsifiers. The obtained solution is sprayed into high speed mixing ethanol or isopropanol to separate out carotenoids as amorphous powders with a particle size of less than 2 μm. The precipitated carotenoids are filtered through a filter film or a sintered filter rod. The filtered cake is washed by ethanol or isopropanol and drained. The filter cake is then added into the aqueous solution containing protective colloid, stirred, homogenized and emulsified. The residual solvents are removed to prepare an aqueous dispersion. Then, the dispersion is sprayed for pelletization. Finally water-dispersible carotenoid preparations can be obtained after fluidization desiccation. The method has the advantages of less residual solvents, rapid removal and high efficiency while the particle size of carotenoid crystal powders is 0.7-0.9 μm and the content of all-trans-isomer is less than 85%.
To increase the content of all-trans-isomer in carotenoid powders, we also proposed that combined antioxidants can be added to improve the double-solvent method (the publication number of the patent is CN101016259A). However, the particle size of carotenoid crystal powders is still 0.7-0.9 μm. The bioavailability still needs improvement.
In US2005/0037115, a preparation method of nano-dispersion of carotenoids is described. Carotenoids are dissolved in a fatty acid ester solvent and the solution is added to an aqueous phase containing dispersant. A nano-dispersion liquid of carotenoids can be obtained after the solvent is evaporated. The solubility of carotenoids is very low in esters, thus, only products with the content of less than 0.5% can be obtained.
Henelyta S. Ribeitro et al. (Food Hydrocolloids 22 (2008) 12-17) adopt acetone as a solvent and PLA or PLGA as a polymer. The polymer and β-carotene are firstly dissolved in acetone. Then the solution is added into the aqueous solution containing gelatin and Tween-20. Nano-β-carotene dispersion is made by using solvent-replacement method. Because the solubility of β-carotene in acetone is very small, the content of β-carotene dispersion is quite low.
Xiaoyun Pan et al. (Journal of Colloid and Interface Science 315 (2007) 456-463) adopt absolute ethyl alcohol as a solvent to dissolve or disperse β-carotene. The solution is added into the aqueous solution containing graft casein. Nano-β-carotene dispersion is made by using solvent-replacement method. Similarly, the solubility of β-carotene in alcohol is very small and the content of β-carotene dispersion is quite low.
C. P. Tan and M. Nakajima (Food Chemistry 92 (2005) 661-671) reported that β-carotene is dissolved in hexane and added to the aqueous solution containing Tween 20. The solution is desolventized in a fluidized bed after pre-emulsion and homogenization to form nano-dispersed system of β-carotene.
The nanocrystallization methods mentioned above have all adopted the solvents in which the solubility of β-carotene is very low, so it is difficult to obtain nano-dispersed β-carotene microcapsules with industrial value.